This application is based on and incorporates herein by reference Japanese Patent Application No. 2001-100499 filed on Mar. 30, 2001.
1. Field of the Invention
The present invention relates to an electric power steering system that transmits power from an electric motor to a steering system to reduce a required steering force, and more particularly, to a device and method for setting steering characteristics of the electric power steering system that compiles steering characteristics in accordance with a driver""s personal preferences.
2. Description of Related Art
An electric power steering system has been disclosed in the prior art as JP-A No. 2000-108918. In this electric power steering system, an angular difference in slip between front and rear wheels of a vehicle is computed for estimation on the basis of a yaw rate signal, steering angle signal, vehicle speed signal, and wheel base. Understeer correction value, oversteer correction value, and counter steer correction values are determined in accordance with the estimate, and a correction signal is generated after correction of a target torque signal on the basis of the correction values.
A correction value for the correction signal can be compiled by multiplying the correction value by a switching means. For this compilation a plurality of correction mode selection keys are provided to select the correction modes suitable for the driver""s driving skill, thereby realizing a steering feeling satisfactory to drivers of different levels of driving skill.
The mode selection system of this electric power steering system, however, is capable of selecting, at most, three to five kinds of modes, and therefore has the disadvantage that delicate characteristics selected will not necessarily suit a driver""s personal preferences. That is, the optimum value of the steering feeling of the electric power steering varies with vehicle model, and vehicle model characteristics depend upon a change of time, payload, driving conditions according to driving purpose, and a driver""s individual characteristics such as age and sex. Only the assist of the motor for reducing the steering force is controlled and, therefore, it is hard to gain a good steering feeling.
Therefore, to gain a good steering feeling, it is necessary to comprehensively adjust an assist characteristic, a disabling characteristic, and a damper characteristic. These characteristics are shown by a line graph having at least approximately seven or eight-point elements. There is, therefore, no easy-to-adjust means for drivers in general.
In view of the above-described disadvantages, it is an object of this invention to provide a device and method for setting steering characteristics of an electric power steering system that is capable of grasping the necessary amount of compilation data as an intuitive or sensorial amount while observing the steering characteristics diagram, and altering and compiling the steering characteristics based on the steering characteristics diagram. It therefore becomes possible for a driver to easily and quickly reset the steering characteristics to varied steering feelings agreeable to the driver""s individual characteristics in accordance with the driver""s preferences and vehicle driving conditions.
In the device for setting the steering characteristics of the electric power steering, a plurality of steering characteristics diagrams prepared in relation to the steering conditions are selected by the steering characteristics diagram selection means. The compilation of the steering characteristics is performed on the steering characteristics diagram while observing the steering characteristics diagram in order to achieve the optimum steering feeling in accordance with a driver""s tastes and tendencies, and driving conditions of a vehicle. The steering characteristics diagram thus compiled is stored and then read in to generate a driving signal. The electric power steering driving motor is controlled by the driving signal, thereby assisting steering operation. The steering characteristics diagram, as described above, is compiled so as to achieve the optimum steering feeling in accordance with the driver""s tastes and tendencies and driving conditions of the vehicle from default characteristics at the time of purchase.
The driver, therefore, can ascertain the necessary amount of compilation as an intuitive or sensorial amount by observing the steering characteristics diagram. The driver can easily and quickly reset various steering feelings suitable to the driver""s individual characters in accordance with his tastes, tendencies, and vehicle driving conditions.
The steering characteristics diagram includes a diagram showing a relationship between the steering torque and the assist current, a diagram showing a relationship between the steering wheel steering angle and the assist current, and a diagram showing a relationship between the angular velocity of the steering wheel and the assist current. The optimum steering feeling suited to a driver""s varied individual characteristics can be precisely set through the compilation of each of these diagrams.
The steering characteristics diagram display means is a diagram display screen or similar device. The steering characteristics diagram compilation means is a device capable of compiling, by the driver""s operation, the steering characteristics diagram on the diagram display screen. This device functions to read the compiled steering characteristics diagram by the steering characteristics diagram reading means. It is, therefore, possible to carry out the compilation on the diagram display screen while observing the steering characteristics diagram.
The device is a pointing device, which changes a position by touching an endpoint of the steering characteristics diagram displayed on the diagram display screen. It is, therefore, possible for the driver to intuitively grasp, compile and recognize the amount of compilation. The pointing device, capable of compiling the steering characteristics diagram, includes a mouse, a trackball, a touch pad, and a touch panel, but may include other types of input devices. Using the pointing device, it is possible to extend, shorten, and move a line between endpoints in the steering characteristics diagram by touching and moving the endpoints by the mouse point, thus intuitively grasping the amount of compilation.
For the compilation of the steering characteristics diagram, there is provided a disabling means for disabling the compiling operation in case the operation goes out of the predetermined normal range of compilation. Therefore, it is possible to prevent abnormal steering without overcompilation exceeding a proper range in the steering characteristics diagram resulting from the driver""s mistake or mis-operation.
The steering characteristics diagram display means and the steering characteristics diagram compilation means are built in such vehicle-mounted products as a car navigation system and a TV, separately from the electric power steering. It is, therefore, unnecessary to separately provide a special member for the compilation of the steering characteristics diagram. Since no special member is separately needed and existing members are usable, the interior space of the vehicle is not required to be reduced, which is advantageous in cost as well.
The steering characteristics diagram display means and the steering characteristics diagram compilation means can be wirelessly linked with the electric power steering driving motor control means. The steering characteristics diagram, therefore, can be remotely controlled in advance for display and compilation from outside the vehicle, e.g., from a driver""s home or office.
By the method for setting the electric power steering characteristics, a plurality of steering characteristics diagrams prepared in relation with the steering conditions are selected and the steering characteristics diagrams thus selected by the steering characteristics diagram selection means are displayed. The driver can execute compilation on the steering characteristics diagram while observing the diagram so as to achieve the optimum steering feeling in accordance with personal tastes and tendencies and the driving conditions of the vehicle. The steering characteristics diagram thus compiled is stored, and then is read out of storage. A driving signal is generated on the basis of the steering characteristics diagram read out, so that controlling the electric power steering driving motor which assists the steering operation can be accomplished.
The steering characteristics diagram, as described above, is compiled to gain the optimum steering feeling, from the default characteristics at the time of purchase, in accordance with the driver""s tastes, tendencies and the driving conditions of the vehicle.
The means for displaying the steering characteristics diagram is a diagram display screen. The steering characteristics diagram compilation means is a device capable of compiling the steering characteristics diagram on the diagram display screen by the driver""s operation. This device functions to operate the steering characteristics diagram reading means to read the diagram after compilation, thereby enabling the compilation of the steering characteristics diagram on the diagram display screen while observing it. The device may be a pointing device, which changes a position by touching end points of the steering characteristics diagram displayed on the diagram display screen. It is, therefore, possible for the driver to intuitively recognize the amount of compilation while sensorially grasping the amount of compilation.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.